Dedupe and clean-up flags

[abourget]

A few issues:

• -indices-store are duplicated (between search-archive and search-indexer)
• -blocks-store are duplicated (between almost all apps, blockmeta, eosws, fluxdb, kvdb, mindreader, relayer, search-live, search-forkresolver)
• --mindreader-oneblock-store-url and --merger-one-block-path are named differently, but refer to the same concept (could be deduped)

If we were to dedupe, then we'd lose the knowledge of which app consumes that flag. How could that be communicated otherwise? Is it important?

I propose a flag called --common-blocks-store instead.